Register 

Defining registers 

Registers in TypoScript can be seen as stack array variables in programming languages. Each register can store a complex TypoScript block. Use LOAD_REGISTER to put a variable to the stack, use RESTORE_REGISTER to pull a variable from the stack and curly braces around a variable name to read the current value of the variable. You need a or a cObject. The registers cannot be read on other places than inside of these cObjects.

Example 

10 = COA
10 {
  ### left menu table column
  10 = LOAD_REGISTER
  10 {
    ulClass = col-left
  }

  ### right menu table column
  20 = LOAD_REGISTER
  20 {
    ulClass = col-right
  }

  30 = HMENU
  30 {
    special = list
    special.value = 1
    1 = TMENU
    # ...
    3 = TMENU
    3 {
      stdWrap {
        preCObject = COA
        preCObject {
          10 = RESTORE_REGISTER
        }
        dataWrap = <ul class="{register:ulClass}">|</ul>
      }
      wrap =
      SPC = 1
      SPC {
        allStdWrap {
          replacement {
            10 {
              search = ---
              replace =
            }
          }
          dataWrap = </ul>|<ul class="{register:ulClass}">
        }
      }
    }
  }
}

This example shows a part of a TypoScript which builds a 2 column menu based on a spacer page. A class is added to the ul tag depending on the value of the register variable ulClass. The first pages will have the class col-left and the pages following the spacer page will get the class col-right.

{register:variablename} returns the "current" value of the variable variablename. A register stack can be like any TypoScript setup.

10 = COA
10 {
  10 = LOAD_REGISTER
  10 {
    ulClass = col-left
    aClass = a-special
    colors {
      chief = red
      servant = white
    }
  }
}

The "current" value is just an internal variable that can be used by functions to pass a single value on to another function later in the TypoScript processing. It is like "load accumulator" in the good old C64 days. Basically you can use a "register" as you like. The TSref will tell if functions are setting this value before calling some other object so that you know if it holds any special information.